The present invention relates to a method of monitoring a deposit in a chamber wherein such processing as etching or CVD is performed, to a method of plasma processing, to a method of dry-cleaning a chamber, and to a semiconductor manufacturing apparatus.
With the increasing miniaturization of semiconductor devices in recent years, the problem of increased investment in plants and equipment has become more conspicuous. To efficiently make profits from recovering the investment, it is essential to reduce production cost and increase production yield. In the process of manufacturing a semiconductor device, in particular, individual process steps and the structure of the semiconductor device have increased in complexity, which inevitably necessitates improved methods of administering and controlling the process. The following are conventional techniques used to administer and control the process of manufacturing semiconductor devices with regard to dry etching for patterning a conductive film and an insulating film.
To implement a conventional method of process administration for dry etching, periodic maintenance is performed with respect to a dry-etching apparatus based on the number of processed wafers (number of lots). Specifically, periodic maintenance is performed with respect to the dry-etching apparatus when the number of processed wafers has reached a given value empirically determined to maintain required etching performance, since the number of particles in the chamber increases with the number of wafers processed in the manufacturing process. Similar process control and administration is performed in another processing using plasma, such as plasma CVD.
In a conventional method of process control, if dry etching is performed to remove a given film in a semiconductor device, e.g., the emission intensity of a specific particle in the plasma varies at the completion of removal of the film in the absence of a material to be processed. When the variation reaches a given value or higher, it is judged that dry etching should be completed.
However, the above conventional method of controlling the dry-etching process has the following problems.
Even if emission light from the specific particle is monitored, it does not reflect the representative state of the entire chamber. For instance, as increases in the number of processed wafers (number of processed lots) change the state of the interior wall of the chamber with time, plasma parameters also change. The changing of the plasma parameters in turn causes variations in etching characteristics. Eventually, when the process control becomes unsuitable for the current state, production yield is lowered. For example, when the state of a deposit on the interior wall of the chamber changes, the concentration (density) of a specific active species in the plasma also changes, resulting in a variation in etching rate and a reduction in etching selectivity. Such deteriorations of the etching characteristics may cause an abrupt processing failure or the like.
On the other hand, the above conventional method of administering the dry-etching process has the following problems.
In the above conventional method, the judgment of whether or not periodic maintenance should be performed is not based on any theoretical endorsement but is based on the empirical parameter of the number of processed wafers, so that it is difficult to attain the intended object successfully. For example, unnecessary maintenance is performed oftentimes. Moreover, the availability of the apparatus is lowered by such a factor as the time required by a dry-etching process, which is performed with respect to a wafer for monitoring in order to check various parameters including the number of particles and etching rate.
The problems as mentioned above arise not only with the dry-etching process but also with all types of processing that may produce a deposit on the interior wall of the chamber, involving or not involving the use of a plasma, such as plasma CVD, CVD not using a plasma, and sputtering.
In the case of dry-cleaning a chamber where cleaning gas is allowed to flow in a chamber to remove a deposit attached on the interior wall of the chamber during plasma processing, the cleaning period has conventionally been set out of experiences so that it is not necessarily optimum. As a result, even after dry cleaning is performed, the number of counted particles is not within speculations so that cleaning should be performed again, which partly contributes to low efficiency and reduced availability of the apparatus.
Although the time at which dry etching should be completed is generally judged through a monitor window, a deposit attached on the inner surface of the monitor window reduces the intensity of light for monitoring, which prevents a correct judgment from being made.